1. Field of the Invention
The present invention relates to an occupant protection device, particularly to an occupant protection device in which air bag bodies are housed in the center pad of a steering wheel.
2. Description of the Related Art
Conventionally, there has been known an occupant protection device in which an air bag body is folded and housed in the center pad of a steering wheel and is expanded toward the driver upon the vehicle experiencing an impact so that the driver is protected against the impact.
Here, the center pad of the steering wheel normally rotates along with the steering wheel in accordance with a driving operation of the driver. For this reason, the air bag body housed in the center pad is formed so as to be circular so that the air bag body can be inflated and expanded with the same shape for any steering angle of the steering wheel. The air bag body formed in a circular shape mainly protects the head of the driver.
In recent years, there is an increasing need for an air bag body housed in a steering wheel, which is capable of protecting not only the head of the driver, but also other body parts of the driver sufficiently. In particular, because the chest of the driver is restrained by a seat belt, a strong pressure may be applied to the chest upon the vehicle experiencing an impact.
As a device capable of protecting not only the head of the driver, but also other body parts of the driver, for example, Japanese Unexamined Patent Application Publication (JP-A) No. 2006-069384 discloses an air bag device for an automobile, in which an air bag body is mounted on a center pad configured not to rotate, the air bag body being formed in such a manner as to include a head protection portion, a chest protection portion, and an abdomen protection portion.
JP-A No. 2006-069384 protects not only the head of the driver but also the chest and abdomen of the driver, however, the same inflation and expansion mode is applied to both the head and chest of the driver.
Normally, the distance between the chest of the driver and the steering wheel is shorter that the distance between the head of the driver and the steering wheel. Therefore, the driver can be more effectively protected against an impact to the vehicle by inflating and expanding the air bag body firstly toward the chest of the driver first which is closer to the steering wheel than the head.
The chest of the driver is restrained by a seat belt. Accordingly, a strong pressure may be applied to the chest of the driver because of an impact caused by a collision of the vehicle. Accordingly, the driver can be more effectively protected against the impact to the vehicle by inflating and expanding the air bag body toward the chest of the driver first.
In some countries where wearing a seat belt is not regulated, a priority is placed on protection of the head of the driver rather than reduction of the above-described pressure on the chest. In such a case, the driver can be more effectively protected against an impact to the vehicle by inflating and expanding the air bag body firstly toward the head of the driver first.
As can be appreciated, in the above-described JP-A No. 2006-069384, since the inflation and expansion mode of an air bag body is not differentiated in accordance with the driver's body part to be protected, there is room for an improvement with regard to effective protection of the driver against an impact to the vehicle.